Many pathogenic microbes and large amounts of organic matter are found in sewage. 

1. During sewage treatment primary sludge is produced. Define Primary sludge.

2. Compare it with activated sludge.

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1 Answers

1. All solids that settle during primary treatment are called primary sludge.

2. During secondary treatment the effluent is passed into a settling tank where the bacterial ‘floes’ are allowed to sediment. This sediment is called activated sludge.

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